Method of producing vanillin



y 1950 k v H. B. MARSHALL EIAL 2,516,827

METHOD OF PRODUCING VANILLIN Filed July 23] 1945 Hakka?) I HTTUE'NEY Patented July 25, 1950 METHOD or PRODUCING VANILLIN Harry Borden Marshall, Toronto, Ontario, and harles Alfred Sankey, S Gatharin s, Ont rio, Canada, assignors to The Ontario Paper Conrpany Limited, Thorold, Ontario, Canada Application July 23, 1945, Serial No. 6063690 3 In Canada July '9, 1945 5 Claims. 1 This invention relates to the production c1 vanillin from lignin-containing substances and especially from the efiluents from acid'chemical proc ss s f r producin p p r p r exampl waste sulphite liquor, and to products derived about the production of vanillin from lignin containing substances under alkaline conditions but, in general the yields obtained have been unsatisfactory, indeed it has even been reported that the yield of vanillin is decreased by the introduction of air into the reaction mixture dur-v ing the course of vanillin production "therefrom. The essence of our present invention lies in the fact that air or oxygen may be employed to great advanta e if it is finely dispersed so as to provide adequate contact with the alkaline lignin-containing liquor under conditions of ressure and temperatu hich are co trolled so as to bring t reaction mi ur o a sumeiently hi h temperature s that the reaction rate is thereby increased and at the same time so that the conditions of oxidat on .are not rendered sufliciently s vere to result in the decomposition of a substantial portion of such vanillin as is. formed.- W hav oun hat action pressures in. he ran 59-2 0 lb- Pe square inch and attemperatures inthe ran ism-200 C... atsueh pressure give hi h y satisrectory yields of vanillin.- Since n acc dan with our invention. th yield of vanil is als dependent on conditions o her than the temperature and pressure in th reaotion vessel, th reaction conditions to obtain optimum yields must be selected with add tional-facto s in m d.

, The time or reaction should be selected havin re ard to the otherconditioos so that: the rec action is stopped when the vanillin content of the reaction mixtureis at or near its maximum; the rate of flow of air or oxygen must be sufficient to promote good agitation and should provide a quantity of oxygen during the reaction period of several times that required to supply 16 grains oxygen (one-gram atom oxygen) per 200 grams lignin (approx. one gram molecule of lignin building unit). The concentration of alkali is also important. With alkali concentrations up to100 grams sodium hydroxide per litre of reaction mixture the vanillin yield increases with increasing concentration. In applying our invention a concentration of alkali will preferably be selected from economic considerations 0 alkali cost versus vanillinyield.

It will be apparent, therefore, that we have discovered a method by means of which vanillin may be obtained from lignin-containing substances at greatly reduced cost, the only auxiliary chemicalsrequired being alkali and air.

It is well known that certain specific oxidizing agents have been used to obtain vanillin from lignin-containing substances. For example, the use of copper sulphate is well known. We have discovered that by using air or oxygen in accordance with our invention and in addition We have als discov r d that a catalyst y be used to increase the yield of vanillin when our invention is mployed To prepare a catalyst such as we prefer to employ, copper sulphate may be added to waste sulphite liquor or to the-liquor remaining after waste sulph t li uo has be n passed thr u a pl nt to p oduce eth a c ho which latter i herein referred to as alcohol plant effluent and sub ect d to an alkaline ox da on w h finel divided air or oxy n un er p essu in cco ance with our present invention, At the conclusion of such oxidation there will be present in the reaction mixture'a sludge containing sub-,-

stantia ly all the copper whi h was added as copper sulphate. This sludge seems to be composed of a mixture of various copper oxides and possibly metallic copper but its exact composition is not known to us. The said sludge may be removed from the reaction mixture by filtration or centrifuging or any other suitable mechanical means. This sludge without any further chemical treatment is a catalyst which, when added to subsequent reaction mixtures in which air or duction of vanillin from the efliuents from acid chemical processes for producing paper pulp as hereinbefore described but also to the production of vanillin from the eflluents from alkaline chem- 5 ical processes for producing paper pulp, such as residual kraft liquor and residual soda liquor. Hitherto the treatment of such alkaline process effluents by oxidation procedures for the production of vanillin has been unsuccessful, only oxygen is used as a primary oxidizing agent in minute quantities of vanillin, if any, being formed.

accordance 'withjour invention; will serve to increase the yield'or-vanillin therein to a higher value than if such catalyst were not present. The sludge recovered from a subsequent reaction may be reused in a succeeding reaction and soon from reaction to reaction. Its efiiciency in such a series of reactions appears to be maintained. We have reused such a catalyst at least five times without diminution of its effect over iThelexamples hereinafter suppliedzwill show that byour' method commerciallysatisfactory yields of vanillin may be obtained from such effluents even when no additional alkali is employed. H The following description of experiments which have been performed by us will serve to illustrate the application of our invention. It is to be understood that our invention is not limited to the materials and conditions described in these and above that of a reasonable experimental experiments which are to be considered as exerror in determining the vanillin formedin each-1 ease. Such continued reuse is of course con tingent on minimizing mechanical loss of, catalyst in the cycle.

The figure shows in diagrammatic form an apparatus whichwe have used in some of our experiments and comprises a bomb" I, into which the reactants are introduced; a cover 2, containing an opening 3, leading to a condensing system 4, y in which vapours from the bomb may be condensed and returned'thereto by reflux through the opening 3, the condensersystem terminating in the control relief valve 5, which limits the maximum pressure in the reaction system to a predetermined value. In the bottom of the bomb 4} I, is a porous plate 6, beneathwhich air or oxygen may be introduced and whichse'rves as a gas diffusing means by which air or oxygen enters the reaction zone in a finely'dispersed'state' The air or oxygen is supplie d from a pressurecylinder 1, through waive, 9, which control the pressure and rate of discharge from the cylinder into the gas diffusing means by'tube l0;

The" bomb is falsoequipped with a pressure gauge" I l, and a thermometer well 12, containing a thermometer 13, by means of which the pressure and temperature of 'the' reaction may be noted. The bomb I, may be heated by any 'convenient means, for example, a gas flame I41 A relief valve 15, is provided for general pressure reduction.

In all experiments cited in this specification the lignin content of lig'nin containing substances was estimated in terms of the methoxy] content thereof." The chemicalgroup 01-1 0, or methox'yl" group, is well knownto be a'fchara cteristic component part of lignin'and'is chemically' determinable with reasonable "accuracy by'well-kn'own analytical procedures. ""It isvalid' to assume that the lignin of a complex mixture containing li'gnin is proportional to the-methoxyl' content thereof. In our experimnts'it isassumed that the ratio of methoxyl contentto lignin' content of an of the mixtures investigated is l5'.5 to 100. Such an assumed ratio is in accordance with currentgoiod chemical usage in dealing with lignin-containing substances. Whether this assumed ratio is or is not numerically correct is immaterial because the ratio of methoxyl"to lignin maybe reasonably assumed to be constantforany given lignin c'ontaining substance. The assumption of'the above ratio will, therefore, serve forpur'poses of obtainmg a valid relative guide to thequantity of 'lignin in lignin containingsubstances.

Ourinvention is applicable not only tdthe pro:

amples only. In the majority of the experiments a; thelignin-containing substance used was alcohol M plant effluent. This is a preferred substance to which our invention may be applied.

E. 'rr'z'1'1tple 1 -'I llustrates the use "of air as oaiz'dz'zz'ng On'ej litre of alcohol'plant effluent was heated with 100 grams of caustic soda in the previously described; apparatus, Throughout the heating cycle asteady flow of compressed air,suflicient to insure good agitatiomwas difiused through the liquid the valve 5 being adjusted to relievegas at 110 lb persquare. inch pressure. No, catalyst orspecial oxidizing agent such ascopper sulphate 'wa present. The apparatus washeated sufficiently so that the reactantsweresubjected to an observed temperature of IBQ-I'ZQ" 'C." The apparatus was maintained under these conditions n three hours. At the conclusion of this treatment', the air (flow was turned' off, the system, was cooled to ja lower temperature thanpits boiling pointgatatmospheric pressurajand the pressure 5 reduced ,to' thatof the' atmosphere by'the relief valve, l5; Theresiduall liquor. was then analysed fforfits vanillin content and the latter"correlated with the .orginal lignin content ithereof A yield of vanillin of 11.5 based on the said lignin con tent was obtained,

Exampllzflllustrdting the use bfsmall queu tity' of copper sulphate hydrate incon iunction az'r cnd nlso illustrating preparation of as one litre of' alcohol plant effluent was heate with grains of causticsoda and 16gra'mscoP- per sulphate hydrate in the previously described so apparatus. As'inExample' 1, air was-dispersed through the reaction zone, with theval ve' 5 adjuste'd to relieve fgas' at" IbL per square inch pre sur the reaeuen time at' an obseiVedFtBmperature o'f lfiil 'l'lfl C. being three hours; The 65 experiment'was concluded with temperature and pressure adjustments as in Example :1 and the reaction mixture removed from the bomb, care being taken to thoroughly wash out a' sludge formed therein; This sludge, as 'her'einbe'fore 7o stated-,"is a catalyst in accordance with our invention and was" removed from the reaction mixture In this experini n't a yield of vanillin was'ob- 'taine equivalent to 14.4% oft-he original lignin At the conclusion "or the experiment-thecatalyst was recovered from the reaction mixture: as in Example 2. In thisexperiment a; yield of vanillin was obtained equivalent to 12.7% of .tlre-original lign-in content of the alcohol plant. effluenn h 1 The catalystrecoveredfromthe. above was reused in a series of experiments in-whichthe conditions of Example 3 were repeated. In this series vanil in yieldsfof f14.s 15.6%, 14.2%, and 13.8 vanillin raiibesedtn tne lignin content) were obtained on the second, third, fourth, and

fifth successive reuse oftheeatalyst, no additional copper sulphate being added in any experiment 'of-thisseries. I

Example 4.Illustrati1tg the use as an oxidizing-agent n One litre of alcohol plant efiluent was hea'ted with IOO'grams of caustidsoda and ld'gram's of copper sulphate hydrate in the previously described apparatus. Oxygen was dispersed through V the'rea'ction zone with the valve adjusted to relieve iga'sat '70 lb. pen'sclilar'ejinch; riressure.

The observed temperature was 151 C. I The reaction time under the above conditions was 1% hours. A yield of vanillin of 12.2% of the lignin content or the 'etov'e'plant em, t w obtained. Example 5.-Illustmting the -use of unzsfte sulphite 1 ;'-'="liquor One litre orwasre sulphite' li'quo'rwe jtreat d g 4 as in Example 2. r

A yield of vanillin was obtained equivalent to 10.8% of the lignin content thereof.

Example 6.Illu'strating the use of soda liquor One litre of a liquor resulting from the production of pulp by the soda process was heated with 12 grams copper sulphate hydrate in the previously described apparatus, no additional alkali being added. The pressure and reaction time and temperature were as in Example 2.

A yield of vanillin was obtained equivalent to 3.8% of the lignin content thereof.

Example 7.-Illustmting the use of kraft liquor One litre of a liquor resulting from the production of pulp by the kraft process was treated as in Example 6.

A yield of vanillin was obtained equivalent to 3.2% of the lignin content thereof.

Example 8.Illustrating the use of wood meal 60 grams spruce wood meal were added to one litre of a solution containing 100 grams caustic soda and sixteen grams copper sulphate hydrate and subjected to the oxidation procedure similarly to Example 2. A vanillin yield corresponding to 13.7% of the lignin content of the wood meal was obtained.

Example 9.-Illustrating the combined effect of pressure-temperature and reaction time on vanillin yield A series of experiments were carried out with a single sample of alcohol Plant efiiuent, with alkali and copper sulphate hydrate as in Example 2 am? with constant air-now! "The pressurewas adjusted to give a seriesof increasing pressures,

the corresponding temperatures beingnoted inv each case. The reaction mixture was maintained for three hours under the stated conditions. vanillin yields were obtained as'f'oll'owsz' Relief Pres- "Temperature ,Vanillin sure Observed Yield.

-l 1' "3i. .l' Lb./sq.iu. C. Per cent 50 142 11.2 :30 15cv q 13. 7 1 10-115 169 14.9 1'3U140 175 l3. 5 1 110; 183 12.1 200 g 189' 12.0

obtained.

Employing. conditions similar to example-.2 witlr a 3 hr. reaction time: and pressure at 119-115 lb.-/sq..in. and using 109 grams caustic; soda. three experiments were performed in whichthe rates oiairflow were respectively 3.3, 6.9,. and. 13.4 cu, ft. per.hour. The vanillin yields obtainedwere 9.6%,, 1&5 and, 14. 5. respectively.

Example 11 .-"IlZu'sl'ratingtheeffect of dllca'li concentration Employing conditions similarv a, with a 3- hr. reaction time and-pressure at 110415 Ila/s q. inand-with constant. air flow, the vanillin yield changed asfollows with alkali concentration:

Alkali concenvanillin tratmsrfiustm yield Grams per liter Per cent reaction vessels and difierent lignin-containing substances that the above results will hold for all cases. For example, it would be incorrect to assume that a pressure rang -115 lb. would necessarily always give a maximum vanillin yield for a 3 hr. reaction period. The examples are illustrative of the yields we have obtained by employing our invention and provide a guide as to the effect of variables which will enable others to apply our invention to maximum advantage in their own case.

When in this specification the word pressure is used it is to be understood that we refer to gauge pressure and not absolute pressure.

The words lignin-containing substances when used herein, have reference to th species of chemical individuals which are present in ligno-cellulose materials and to which the word lignin is applied including derivatives of the same which result from chemical processes for assess? producing wood pulp and; arepresent in the re sidua-l liquors from said processes. a

The chemical identity and nature ofligninas originally present in .ligno-cellulose materials and in the species lignin-containing substances, has not been established. The scopeof the term lignin as herein used, may be defined as by Brauns in Cellulose and its Derivatives, edited. by Ott, Interscience Publishers Inc., first edition 1943, page 449, line 7 ff. it

What we claim as our invention is:

1. A catalyst which assists in the production of vanillin consisting of the sludge residual in a reaction mixture in which vanillin has been produced by subjecting, to the action of a finely ll! dispersed gas containing free gaseous oxygen,

lignin-containing' substances in an alkaline mediumvto which has been added copper sulphate under conditions of temperature in excess of 140 C; and partial pressure of oxygen ofless than 20 go 1 lb. per sq. in.

2. A method of producing vanillin which con sists in subjecting to the action of a finely dispersed gas containing free gaseous oxygen a re action mixture comprising lignin-containing sub- 35 stances in an alkaline medium to which has been added copper sulphate, separating the residual sludge therefrom, adding said sludge to -a reaction mixture containing lignin-containing' substances in' an alkaline"medium and subjecting 30 persed gas containing free aqueous oxygen a re- 5 action mixture comprising lignin-containing substances in an alkaline medium to which has been added copper sulphate, separating the residual sludge therefrom, adding said sludge to a re-- stances in an alkaline""medium,and subjecting such combinedmaterials-to the action of a finely dispersed gas containing tree gaseous oxygen, recovering-the sludge fromsaid process and repeatedly reusing said sludge as a catalyst in the productio'n of vanillin according to the said method.*-'-

'4.-A method of producing vanillin according to claim 3 in'which the'lignin-containing substance consists of waste sulphite liquor. 5. A method of producing vanillin according to claim 3 in which the-lignin-containing substance is'theeflluent from a process in which waste sulphit'e liquor-has been so treated that as a result the' fermentable sugar content thereof has been substantially reduced.

' REFERENCES CITED The following references are of record in th file of this patent: I A. g

' UNITED STATES PATENTS Number Name I Date 2 2,434,626 Salvesen Jan. 13, 1948 FQREIGN PATENTS Number Country- Date 513,755 Germany Dec. 14, 1931 Germany-,- Dec. 14, 1931 537,845 r cvrnna REFERENCES ser. No.318,386 ,Freudenberg et al. (A. no), pub. April 20, 1943.

Lautsch et. al., Angewandte Chemie, vol. 53, pages 450-452, September 28, 1940.

1 Pearl fJour. Am.:chem. $00.," vol 64, pages action mixture containing lignin-cont'ainingsu 4 14294431. 

1. A CATALYST WHICH ASSISTS IN THE PRODUCTION OF VANILLIN CONSISTING OF THE SLUDGE RESIDUAL IN A REACTION MIXTURE IN WHICH VANILLIN HAS BEEN PRODUCED BY SUBJECTING, TO THE ACTION OF A FINELY DISPERSED GAS CONTAINING FREE GASEOUS OXYGEN, LIGNIN-CONTAINING SYBSTANCES IN AN ALKALINE MEDIUM TO WHICH HAS BEEN ADDED COPPER SULPHATE UNDER CONDITIONS OF TEMPERATURE IN EXCESS OF 140* C. AND PARTIAL PRESSURE OF OXYGEN OF LESS THAN 20 LB. PER SQ. IN. 